The invention is directed to apparatus and methods for applying liquid materials to a web and further processing the web by application of additional liquid material to the web through an electrostatic field.
Conventional web-offset printing presses utilize heat-settable ink that is set or cured by heat after the ink is printed onto a paper web. The curing of the ink is typically done by passing the web through a dryer, which causes the temperature of the web to be raised to a relatively high temperature, such as in the range of 250.degree. to 320.degree. F. (Fahrenheit). After it passes from the dryer, the hot web must be cooled to allow effective processing of the web in subsequent operations.
FIG. 1 schematically illustrates a prior art web-offset printing press 10 of the type described generally above. Referring to FIG. 1, the prior art printing press 10 incorporates a plurality of rotatable printing cylinders 12, 14, each of which applies an image to a paper web 16 using a heat-settable ink. The paper web 16, which is guided by a number of rollers 18, passes through the printing press 10 from left to right, as indicated by the arrow shown in FIG. 1.
After the ink is applied by the printing cylinders 12, 14, the web 16 is passed through a dryer 20, which sets the ink by raising the temperature of the web 16 to a relatively high temperature. After passing through the dryer 20, the web 16 is passed over a plurality of chill rolls 22 to cool the web 16. Heat from the web 16 is absorbed by relatively cool water which is piped through the chill rolls 22. After passing through all of the chill rolls 22, the web 16 is at or close to (within 10.degree. F.) room temperature.
After being heated by the dryer 20 and cooled by the chill rolls 22, the paper web 16 has very little moisture content. Consequently, after being cooled by the chill rolls 22, the web 16 is fed to an electrostatic remoistener 24 which adds moisture back to the web 16. The remoistener 24 is provided with a plurality of spray nozzles (not shown) for spraying water droplets onto the paper web 16 and a plurality of field directors (not shown) on each side of the web 16 for generating a directed electrostatic field. The field directors on one side of the web 16 are maintained at a high voltage relative to the field directors on the other side of the web 16, and water is sprayed through the electrostatic field so that the water droplets travel within a confined path between the spray nozzles and the paper web 16.